Control method and device for a power-converting module that drives a light-emitting component

ABSTRACT

A control device, which controls a power-converting module that is coupled to a light-emitting component, includes a duration detecting unit and a control signal generator. The duration detecting unit compares the duration of a predetermined logic state of a pulsating input dim control signal with a reference time period. The control signal generator is enabled by the duration detecting unit so as to generate a control signal that enables the power-converting module to generate a drive voltage for driving the light-emitting component when the duration of the predetermined logic state is not longer than the reference time period. The duration detecting unit disables the control signal generator to disable the power-converting module when the duration of the predetermined logic state is longer than the reference time period.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/919,015, filed on Aug. 16, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method and device for controllinglight-emitting components, more particularly to a control method anddevice for controlling a power-converting module that drives alight-emitting component.

2. Description of the Related Art

A conventional driver integrated circuit (driver IC) for driving alight-emitting diode (LED) must also provide a function of controllingthe brightness output of the LED in a linear and stable manner so thatan electronic apparatus that uses the LED as a backlighting source, suchas a mobile phone, a personal digital assistant (PDA), etc., can have astable and good display screen. Currently, a method widely used in thistype of driver IC relies upon pulse signals for controlling thebrightness output of the LED. In particular, to achieve a desiredbrightness, pulse signals with a predetermined frequency are fed to thedriver IC so as to alternately turn on and turn off the LED. When thefrequency of the pulse signals becomes higher, the brightness output ofthe LED becomes brighter. On the other hand, when the frequency of thepulse signals becomes lower, the brightness output of the LED becomesdimmer. However, to operate the driver IC in this manner, aside from thefact that a larger amount of power is consumed, a side effect ofelectromagnetic interference is also encountered due to the rapid turnon and turn off activity of the driver IC, which has an adverse effecton other electronic components. Therefore, to overcome the aforesaiddrawback, a pulse-width-modulation (PWM) control circuit has beenproposed heretofore for controlling the driver IC so as to adjust thedrive current that is supplied by the driver IC to the LED, therebycontrolling the brightness output of the LED.

When the conventional PWM control circuit is in use, an enable signal isprovided to activate the driver IC, and a brightness control signal isprovided to control driving of the LED. The conventional driver IC hasseparate input terminals for receiving the enable signal and thebrightness control signal, respectively. In view of the current trendtoward miniaturization of electronic components, a reduction in theterminal count of the driver IC is highly desirable.

SUMMARY OF THE INVENTION

Therefore, the object of the present invention is to provide a controlmethod and device for controlling a power-converting module that drivesa light-emitting component so as to overcome the aforesaid drawbacksassociated with the prior art.

According to one aspect of the present invention, there is provided acontrol method for controlling a power-converting module that is coupledto a light-emitting component. The control method comprises the stepsof:

a) comparing duration of a predetermined logic state of a pulsatinginput dim control signal with a reference time period;

b) when the duration of the predetermined logic state of the pulsatinginput dim control signal is not longer than the reference time period,generating a pulse-width-modulated control signal that corresponds tothe pulsating input dim control signal and that is provided to thepower-converting module, thereby enabling the power-converting module togenerate a drive voltage for driving the light-emitting component togenerate a brightness output that corresponds to the pulsating input dimcontrol signal; and

c) when the duration of the predetermined logic state of the pulsatinginput dim control signal is longer than the reference time period,disabling the power-converting module to turn off the light-emittingcomponent.

According to another aspect of the present invention, there is provideda control device for controlling a power-converting module that iscoupled to a light-emitting component. The control device comprises aduration detecting unit and a control signal generator.

The duration detecting unit is adapted for comparing duration of apredetermined logic state of a pulsating input dim control signal with areference time period.

The control signal generator is coupled to the duration detecting unit,and is enabled by the duration detecting unit so as to generate apulse-width-modulated control signal that corresponds to the pulsatinginput dim control signal and that is to be provided to thepower-converting module, thereby enabling the power-converting module togenerate a drive voltage for driving the light-emitting component togenerate a brightness output that corresponds to the pulsating input dimcontrol signal, when the duration detecting unit determines the durationof the predetermined logic state of the pulsating input dim controlsignal to be not longer than the reference time period.

The duration detecting unit disables the control signal generator so asto disable the power-converting module and turn off the light-emittingcomponent when the duration detecting unit determines the duration ofthe predetermined logic state of the pulsating input dim control signalto be longer than the reference time period.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will becomeapparent in the following detailed description of the preferredembodiment with reference to the accompanying drawings, of which:

FIG. 1 is a schematic circuit block diagram showing the preferredembodiment of a control device for controlling a power-converting modulethat is coupled to a light-emitting component; and

FIG. 2 illustrates a pulsating input dim control signal suitable for usein the preferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, the preferred embodiment of a control device 1according to the present invention is adapted for controlling apower-converting module 2 that is coupled to a light-emitting component3, such as an LED, LCD or OLED. The control device 1 comprises aduration detecting unit 11 and a control signal generator 12.

The duration detecting unit 11 is adapted for comparing the duration(t₂) of a predetermined logic state of a pulsating input dim controlsignal (S_(dim)) with a reference time period (t₃). Referring to FIG. 2,in this embodiment, since the duration detecting unit 11 is designed tobe low active, the predetermined logic state is a low logic state of thepulsating input dim control signal (S_(dim)). It should be noted thatthe duration detecting unit 11 may be designed to be high active. Inthis case, the operating principles to be described hereinbelow are tobe performed inversely.

The control signal generator 12 is coupled to the duration detectingunit 11, and is enabled by the duration detecting unit 11 so as togenerate a pulse-width-modulated control signal (S_(ctrl)) thatcorresponds to the pulsating input dim control signal (S_(dim)) and thatis to be provided to the power-converting module 2, thereby enabling thepower-converting module 2 to generate a drive voltage (V_(o)) fordriving the light-emitting component 3 to generate a brightness outputthat corresponds to the pulsating input dim control signal (S_(dim)),when the duration detecting unit 11 determines the duration (t₂) of thepredetermined logic state of the pulsating input dim control signal(S_(dim)) to be not longer than the reference time period (t₃).

The duration detecting unit 11 disables the control signal generator 12so as to disable the power-converting module 2 and turn off thelight-emitting component 3 when the duration detecting unit 11determines the duration (t₂) of the predetermined logic state of thepulsating input dim control signal (S_(dim)) to be longer than thereference time period (t₃).

The control device 1 further comprises a signal-filtering unit 13 forgenerating a modulator control signal (S_(mod)) that corresponds to areference voltage (V_(ref)) amplified by a gain (G) equal to an averagevalue (or DC value) of the pulsating input dim control signal (S_(dim)).

The control signal generator 12 is coupled to the signal-filtering unit13, and includes a pulse-width modulator 121 that receives the modulatorcontrol signal (S_(mod)), and an oscillator 122 that is coupled to thepulse-width modulator 121 and that provides an oscillator signal to thepulse-width modulator 121. The pulse-width modulator 121 generates thepulse-width-modulated control signal (S_(ctrl)) from the modulatorcontrol signal (S_(mod)) and the oscillator signal. In particular, ifthe voltage level of the modulator control signal (S_(mod)) is higher,the duty cycle of the pulse-width-modulated control signal (S_(ctrl))will be lower. Otherwise, the duty cycle of the pulse-width-modulatedcontrol signal (S_(ctrl)) will be higher.

The power-converting module 2 includes a converting unit 21 and anoutput filtering unit 22 coupled to the converting unit 21. Theconverting unit 21 is adapted to receive an input voltage (V_(in)) andthe pulse-width-modulated control signal (S_(ctrl)), and converts theinput voltage (V_(in)) into a pulse-shaped high-frequency voltage withreference to the pulse-width-modulated control signal (S_(ctrl)). Thepulse-shaped high-frequency voltage is subsequently provided to theoutput filtering unit 22 for filtering so as to generate the directcurrent drive voltage (V_(o)) that is supplied to the light-emittingcomponent 3. The voltage level of the drive voltage (V_(o)) isproportional to the duty cycle of the pulse-width-modulated controlsignal (S_(ctrl)). That is, the higher the duty cycle of thepulse-width-modulated signal control (S_(ctrl)), the higher will be thevoltage level of the drive voltage (V_(o)). Accordingly, the lower theduty cycle of the pulse-width-modulated signal control (S_(ctrl)), thelower will be the voltage level of the drive voltage (V_(o)). Therefore,through the pulsating input dim control signal (S_(dim)), thepulse-width-modulated control signal (S_(ctrl)) can be controlled sothat the desired drive voltage (V_(o)) can be generated from the inputvoltage (V_(in)).

Preferably, the light-emitting component 3 is coupled to a groundedfeedback unit 4, such as a feedback resistor. The brightness output ofthe light-emitting component 3 depends on the amount of drive currentflowing therethrough. Since the drive current also flows through thefeedback unit 4, a feedback signal (V_(fb)) that is indicative of theamount of current flow through the light-emitting component 3 can beobtained from the feedback unit 4. The pulse-width modulator 121 iscoupled to the feedback unit 4, receives the feedback signal (V_(fb)),and stabilizes the pulse-width-modulated control signal (S_(ctrl)) withreference to the feedback signal (V_(fb)) in a manner well known in theart. As a result, the drive voltage (V_(o)) can be maintained at thedesired voltage level to ensure a stable brightness output from thelight-emitting component 3.

It should be noted herein that the control device 1 is capable of beingrealized in the form of an integrated circuit. Moreover, sinceadjustment of the drive voltage (V_(o)) by the power-converting module 2through pulse-width-modulation control is performed in a manner wellknown to those skilled in the art, further details of the same will bedispensed herewith for the sake of brevity.

In sum, to adjust the brightness output of the light-emitting component3 through the control device 1 of the preferred embodiment, the durationdetecting unit 11 first compares the duration (t₂) of the predeterminedlogic state (e.g., the low logic state) of the pulsating input dimcontrol signal (S_(dim)) with the reference time period (t₃). When theduration (t₂) of the predetermined logic state of the pulsating inputdim control signal (S_(dim)) is longer than the reference time period(t₃), the duration detecting unit 11 disables the control signalgenerator 12 so as to disable the power-converting module 2 and turn offthe light-emitting component 3. Otherwise, the control signal generator12 is enabled by the duration detecting unit 11 so as to generate thepulse-width-modulated control signal (S_(ctrl)) that corresponds to themodulator control signal (S_(mod)) from the signal-filtering unit 13,which in turn corresponds to the pulsating input dim control signal(S_(dim)), and that is provided to the power-converting module 2. Uponreceipt of the pulse-width-modulated control signal (S_(ctrl)), thepower-converting module 2 is enabled to generate the drive voltage(V_(o)) for driving the light-emitting component 3 to generate abrightness output that corresponds to the pulsating input dim controlsignal (S_(dim)). In the view of the abovementioned construction, areduction in terminal count is possible using the control device 1 ofthis invention.

While the present invention has been described in connection with whatis considered the most practical and preferred embodiment, it isunderstood that this invention is not limited to the disclosedembodiment but is intended to cover various arrangements included withinthe spirit and scope of the broadest interpretation so as to encompassall such modifications and equivalent arrangements.

1. A control method for controlling a power-converting module that is coupled to a light-emitting component, comprising the steps of: a) comparing duration of a predetermined logic state of a pulsating input dim control signal with a reference time period; b) when the duration of the predetermined logic state of the pulsating input dim control signal is not longer than the reference time period, generating a modulator control signal that corresponds to a reference voltage amplified by a gain equal to an average value of the pulsating input dim control signal, generating a pulse-width-modulated control signal from the modulator control signal, and providing the pulse-width modulated control signal to the power-converting module, thereby enabling the power-converting module to generate a drive voltage for driving the light-emitting component to generate a brightness output that corresponds to the pulsating input dim control signal; and c) when the duration of the predetermined logic state of the pulsating input dim control signal is longer than the reference time period, disabling the power-converting module to turn off the light-emitting component.
 2. The control method as claimed in claim 1, wherein step b) further includes: stabilizing the pulse-width-modulated control signal with reference to a feedback signal that is indicative of amount of current flow through the light-emitting component.
 3. The control method as claimed in claim 1, wherein the pulse-width-modulated control signal is not generated in step c) so as to disable the power-converting module. 